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<p>The effect of welding heat input on bainite transformation in the coarse-grained heat-affected zone of P11 steel was investigated using a combination of in situ and ex situ characterization techniques. At a heat input of 15&#xa0;kJ/cm, rapid cooling produced a hard, fine lath bainite-dominated microstructure, with lath growth primarily constrained by prior austenite grain boundaries and ghost traces. This microstructure exhibited a high fraction of high-angle grain boundaries at 72.6% and a deformed grain fraction of 46.3%. In contrast, at a heat input of 55&#xa0;kJ/cm, a softer, coarse granular bainite-dominated microstructure was obtained. High-temperature recovery promoted the development of dense subgrain networks that impeded lath propagation, shifting the transformation toward a slower, cooperative nucleation mode. This transition was accompanied by a marked reduction in high-angle grain boundaries fraction to 37.1% and a substantial increase in substructured grain fraction to 87.9%. These findings elucidate the relationships among heat input, transformation kinetics, and microstructural characteristics, providing a theoretical basis for optimizing welding parameters in P11 steel.</p>

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Unveiling Bainitic Microstructure Evolution in the Coarse-Grained Heat-Affected Zone of P11 Steel: Effects of Welding Heat Inputs via In Situ and Ex Situ Characterization

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Aidi Zhang,
  • Yang Shen

摘要

The effect of welding heat input on bainite transformation in the coarse-grained heat-affected zone of P11 steel was investigated using a combination of in situ and ex situ characterization techniques. At a heat input of 15 kJ/cm, rapid cooling produced a hard, fine lath bainite-dominated microstructure, with lath growth primarily constrained by prior austenite grain boundaries and ghost traces. This microstructure exhibited a high fraction of high-angle grain boundaries at 72.6% and a deformed grain fraction of 46.3%. In contrast, at a heat input of 55 kJ/cm, a softer, coarse granular bainite-dominated microstructure was obtained. High-temperature recovery promoted the development of dense subgrain networks that impeded lath propagation, shifting the transformation toward a slower, cooperative nucleation mode. This transition was accompanied by a marked reduction in high-angle grain boundaries fraction to 37.1% and a substantial increase in substructured grain fraction to 87.9%. These findings elucidate the relationships among heat input, transformation kinetics, and microstructural characteristics, providing a theoretical basis for optimizing welding parameters in P11 steel.